Towards a coherent program to establish the systematic errors

1. Towards a coherent program to establish the systematicerrors in the long baselineexperiments The community should support a program for detector R&D and critical measurements like cross sections and hadron production. The CERN neutrino platform is an important basis to fulfil these goals. The European members of the ICFA Neutrino panel P5 report NuSTORMis a proposal for a small muon storage ring to produce ~GeVneutrinos and antineutrinos with the advantage of a precisely known flux. The facility would also serve as an intense source of low-energy muons and serve as a technology demonstrator for a future neutrino factory. The physics reach of this program includes sensitive sterile neutrino searches and precision neutrino cross-section measurements. Although the concept is attractive as a first step towards a neutrino factory and as a means to reduce the beam-related systematic errors for LBNF, the high cost makes it impossible to pursue at the same time as PIP-II and LBNF, which are the primary objectives. While the agencies and the laboratory directors recognise that to realise the success of the above projects there will be a need for investment in theory and necessary support measurements, this document should not be interpreted as a funding endorsement.

2. consequences of large theta_13. Superbeam (Water Cherenkov vs Liquid Argon) vs betabeam / neutrino factory -1- golden channel signal e is large ( 5%)  backgrounds are not so important (water OK)  signal canbeseen and CP violation measured at conventionalsuperbeam. -2- CP asymmetryissmall (~0.3 x sin ) for first maximum  Systematicsfromdetection (efficiency x cross-sections) become dominant (to demonstrate «betterthan 5%» on e /isnot trivial) => ICFA panel : needcomprehensive program to tacklesystematicerrors. Among best possibilities: muon storage ring nustormfor cross-section and calibration withLiquid Argon or Water Cherenkov detector (as the case maybe). Not in P5, US wont do it. Mypersonnal opinion: thiscouldbe a fantastic contribution from CERN.

3. HYPERK (WC, 300km optimized off-axis narrow band) New near detector to reducesystematics! LBNE (Larg, 1300km OptimizedWide Band) Also to consider: timing, political situation, astroparticle and proton decaycapabilities.

4. Complementarity -1- HyperKis the natural continuation to T2K We have invested in NA61, and in the near detectors of T2K It is the most sensitive proposal for the observation of CP violation in neutrino oscillations and for a large part of underground physics (proton decay, atmospheric, solar and supernovae neutrinos) .... and the most straight-forwardtechnology -2- itis not completehowever and thereis a physics case for a complementaryexperimentthatwoulddetermine unambiguously the value of CP and the mass hierarchy, complete the observations of oscillations involving tau leptons and mattereffects {LBNO; LBNE} . This requires a more sensitive technology (Liq. Argon) , in need of R&D and experience(and probably a longer time scale) The pathis not unique and includesfocused R&D (WA105) and application + experience on running experiments(microboone)

7. Zooming on «parametric» systematic errors As expected13dominates

8. Zooming on detection-related systematics As expectede dominates! CP Emphasizes once more the importance to know cross-section x efficiency for the e (in far detector) /  (in near detector)

10. whatisneeded to keepsystematics at lowlevel in the measurements of eoscillation probability -- needhadroproductionexperiment for near/far flux ratio NA61/SHINE -- needenergy calibration of electrons vs muons -- need cross-section measurementsespecially to establish ratio ()xeff /(e)xeff for neutrino and antineutrino (especially sensitive for CP violation) -?- istheory/experimentotherwise able to provide cross-section ratio and precise eventgenerator -- need to understandresolution on reconstruction of E esp. sensitive for 23

11. CP asymmetry decreases as sin2213 increases… Systematics! First maximum • Challenge of precision! • Flux and cross-sections must be known to <<5% • hadro production experiments (NA61@CERN) + near detectors  cross-sections to 5% • needed to measure cross-sections • to 1% precision  mini neutrino factory (first step muon storage ring) • Old idea, re-publicized in 2009. Now proposed under name nuSTORM Bross@NUFACT11 TASD, LArg…

12. PRACTICALITIES

14. Implementation, at CERN: • Principal issue: • SPS spill is 10 μs: • Implies bend for proton or pion beam • Or development of fast extraction • Two options: • NA implementation: • Possible exploitation of synergies with ICARUS/NESSiE • NA-to-WA implementation: • Advantage is proton/pion bend not required; • Longer baseline must be tuned to larger muon energy (possibly an advantage too)

15. Implementation, at CERN: • Principal issue: • SPS spill is 10 μs: • Implies bend for proton or pion beam • Or development of fast extraction • Two options: • NA implementation: • Possible exploitation of synergies with ICARUS/NESSiE • NA-to-WA implementation: • Advantage is proton/pion bend not required; • Longer baseline must be tuned to larger muon energy (possibly an advantage too) North area extension

16. Event rates per 100ton at the near detector station arXiv:1308.6822v1

17. by varying the muon beamenergy, canaccess a narrow band beam  evaluateresolution and calibration of neutrino energy reconstruction

18. It seemsthataddingprecise signal cross-section ( =. ) -- for near detector normalizationchannel ( or ) -- and far detector signal channel (eore) canimprove the final reach of a long baselineexperimentconsiderably. nuSTORMexposure of near detector and far detector prototype -- size 1-100 tons shouldprovide the proper data set for 1% meaasurement of cross-sections. It fitswell in a stagedapproachwith excellent physics output ateach stage desired date = if possible a few yearsbefore the LBL experimentstarts.

19. Personalcomments on nuSTORM: nuSTORM does four things: 1. a first experience with running a production muon storage ring!2. provide beams of nu_e, antinu_e, nu_mu and antinu_mu with fluxes known to <1% precision and measurements of neutrino cross-sections with that kind of precision for these four species of neutrinos and for any detector that can distinguish e's from mu's, Liquid Argon in particular. 3. possibly provide a very sensitive search for the particular light sterile neutrino that is claimed to have been observed by the LSND experiment at Los Alamos. My fear is that this observation is very weak and controversial, and furthermore maybe killed long before nustorm can be built, by e.g. the LAR1 program on the BooNE beam at Fermilab. 4. also provide a high flux of muons for the sake of doing muon cooling R&D Because of property 2. I would argue that nuSTORM should be integral part of the long baseline neutrino program aiming at the discovery and study of CP violation with conventional neutrino beams (HyperK, LBNE or LBNO). The desirable commissioning timescale is "early 2020's". nuSTORM would be a fantastic contribution from CERN.

20. Conclusions I believeweshouldlook at nuSTROMwithgreatinterest For instance implementationat CERN should point to Larg prototype! This couldbe a very important (and interesting) contribution to a long baseline program.